Method of subatmospheric plasma-enhanced ald using capacitively coupled electrodes with narrow gap

ABSTRACT

A method for depositing a film by plasma-enhanced subatmospheric-pressure atomic layer deposition (subatmospheric PEALD) is conducted using capacitively coupled parallel plate electrodes with a gap of 1 mm to 5 mm, wherein one cycle of subatmospheric PEALD includes: supplying a precursor in a pulse to the reaction chamber; continuously supplying a reactant to the reaction chamber; continuously supplying an inert gas to the reaction chamber; continuously controlling a pressure of the reaction chamber in a range of 15 kPa to 80 kPa; and applying RF power for glow discharge in a pulse to one of the parallel plate electrodes.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally relates to a method of plasma-enhancedatomic layer deposition (PEALD), particularly a method of subatmosphericPEALD using capacitively coupled electrodes with a narrow gap.

Description of the Related Art

Conventionally, in plasma-enhanced atomic layer deposition (PEALD), aplasma is generated in between two parallel plate electrodes that arespaced about 1 to 5 cm apart, from a source gas at low pressure (1 to 10mTorr) (Stephan Heil, “Plasma-Assisted Atomic Layer Deposition of MetalOxides and Nitrides”, Technische Universiteit Eindhoven, 2007, p. 6).Since PEALD uses a self-limiting adsorption reaction process,conformality of a thin film deposited by PEALD is high. However, asdevice miniaturization progresses, PEALD faces a problem that filmproperties such as chemical resistance and dry etching resistance of afilm deposited on a sidewall of a fine trench are inferior to those of afilm deposited on a flat surface due to uneven ion bombardment by aplasma where ion bombardment is weaker at the sidewall than that on theflat surface.

Any discussion of problems and solutions in relation to the related arthas been included in this disclosure solely for the purposes ofproviding a context for the present invention, and should not be takenas an admission that any or all of the discussion was known at the timethe invention was made.

SUMMARY OF THE INVENTION

In some embodiments of the present invention, thermal plasma isgenerated by PEALD at subatmospheric pressure using a conventional orany suitable capacitively coupled plasma (CCP) apparatus wherein processpressure is significantly increased and the gap between two parallelplate electrodes is significantly narrowed to 5 mm or less. In someembodiments, silicon-based insulation films or metal-based insulationfilms can effectively be deposited using subatmospheric PEALD, whereinproperties of a film deposited at the sidewall of a trench or otherpatterned recess are remarkably improved, and, for example,surprisingly, wet etch rate (WER) of the sidewall film can be renderedapproximately the same as that of top (blanket) film. In someembodiments, a carbon-based film which normally shows poor conformalitydue to insufficient ion bombardment at the sidewall even using an ALDmode can be deposited by subatmospheric PEALD, wherein the conformalityof a deposited carbon-based film can significantly be improved.

For purposes of summarizing aspects of the invention and the advantagesachieved over the related art, certain objects and advantages of theinvention are described in this disclosure. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention. The drawings are greatlysimplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomiclayer deposition) apparatus for depositing a dielectric film usable inan embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supplysystem using a flow-pass system (FPS) usable in an embodiment of thepresent invention.

FIG. 2 shows a schematic process sequence of subatmospheric PEALD in onecycle according to an embodiment of the present invention using oneprecursor wherein a cell in gray represents an ON state whereas a cellin white represents an OFF state, and the width of each cell does notrepresent duration of each process.

FIG. 3 shows a schematic process sequence of subatmospheric PEALD in onecycle according to an embodiment of the present invention using twoprecursors wherein a cell in gray represents an ON state whereas a cellin white represents an OFF state, and the width of each cell does notrepresent duration of each process.

FIG. 4 shows a schematic process sequence of subatmospheric PEALD in onecycle according to another embodiment of the present invention using twoprecursors wherein a cell in gray represents an ON state whereas a cellin white represents an OFF state, and the width of each cell does notrepresent duration of each process.

FIG. 5 shows a schematic process sequence of subatmospheric PEALD in onecycle and a schematic process sequence of subsequent subatmosphericsurface treatment in one cycle according to an embodiment of the presentinvention wherein a cell in gray represents an ON state whereas a cellin white represents an OFF state, and the width of each cell does notrepresent duration of each process.

FIG. 6 shows a schematic process sequence of subatmospheric surfacetreatment in one cycle according to an embodiment of the presentinvention wherein a cell in gray represents an ON state whereas a cellin white represents an OFF state, and the width of each cell does notrepresent duration of each process.

FIG. 7 is a schematic representation of a subatmospheric PEALD apparatusfor depositing a dielectric film usable in an embodiment of the presentinvention.

FIG. 8 is a flowchart illustrating a process sequence of subatmosphericPEALD according to an embodiment of the present invention.

FIG. 9 shows minimum RF power required for ignition of a plasma atpressures of 0.5 kPa and 30 kPa when varying concentration of oxygen ina reactant gas, wherein (a) shows when the reactant gas contains He, and(b) shows when the reactant gas contains Ar.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid andmay be constituted by a single gas or a mixture of gases, depending onthe context. Likewise, an article “a” or “an” refers to a species or agenus including multiple species, depending on the context. In thisdisclosure, a process gas introduced to a reaction chamber through ashowerhead may be comprised of, consist essentially of, or consist of asilicon-containing precursor and an additive gas. The additive gasincludes a gas for oxidizing and/or nitriding the precursor when RFpower is applied to the additive gas. The precursor and the additive gascan be introduced as a mixed gas or separately to a reaction space. Theprecursor can be introduced with a carrier gas such as a rare gas. A gasother than the process gas, i.e., a gas introduced without passingthrough the showerhead, may be used for, e.g., sealing the reactionspace, which includes a seal gas such as a rare gas. In someembodiments, “film” refers to a layer continuously extending in adirection perpendicular to a thickness direction substantially withoutpinholes to cover an entire target or concerned surface, or simply alayer covering a target or concerned surface. In some embodiments,“layer” refers to a structure having a certain thickness formed on asurface or a synonym of film or a non-film structure. A film or layermay be constituted by a discrete single film or layer having certaincharacteristics or multiple films or layers, and a boundary betweenadjacent films or layers may or may not be clear and may be establishedbased on physical, chemical, and/or any other characteristics, formationprocesses or sequence, and/or functions or purposes of the adjacentfilms or layers. Further, in this disclosure, any two numbers of avariable can constitute a workable range of the variable as the workablerange can be determined based on routine work, and any ranges indicatedmay include or exclude the endpoints. Additionally, any values ofvariables indicated (regardless of whether they are indicated with“about” or not) may refer to precise values or approximate values andinclude equivalents, and may refer to average, median, representative,majority, etc. in some embodiments. Further, in this disclosure, theterms “constituted by” and “having” refer independently to “typically orbroadly comprising”, “comprising”, “consisting essentially of”, or“consisting of” in some embodiments. In this disclosure, any definedmeanings do not necessarily exclude ordinary and customary meanings insome embodiments.

In the present disclosure where conditions and/or structures are notspecified, the skilled artisan in the art can readily provide suchconditions and/or structures, in view of the present disclosure, as amatter of routine experimentation.

In all of the disclosed embodiments, any element used in an embodimentcan be replaced with any elements equivalent thereto, including thoseexplicitly, necessarily, or inherently disclosed herein, for theintended purposes. Further, the present invention can equally be appliedto apparatuses and methods.

The embodiments will be explained with respect to preferred embodiments.However, the present invention is not limited to the preferredembodiments.

In an embodiment, a method for depositing a film by plasma-enhancedsubatmospheric-pressure atomic layer deposition (subatmospheric PEALD),comprises: (1) placing a substrate between capacitively coupled parallelplate electrodes in an evacuatable reaction chamber, wherein a distancebetween the parallel plate electrodes is in a range of 1 mm to 5 mm; and(2) depositing a film having a desired thickness (e.g., 2 to 50 nm,typically 10 to 30 nm) on the substrate by plasma-enhanced atomic layerdeposition (PEALD), each cycle of which comprises: (i) supplying aprecursor in a pulse to the reaction chamber; (ii) continuouslysupplying a reactant to the reaction chamber; (iii) continuouslysupplying an inert gas to the reaction chamber; (iv) continuouslycontrolling a pressure of the reaction chamber in a range of 15 kPa to80 kPa; and (v) applying RF power for glow discharge in a pulse to oneof the parallel plate electrodes, wherein the pulse of supplying theprecursor and the pulse of applying RF power do not overlap.

In some embodiments including the above embodiment, the distance betweenthe parallel plate electrodes may be defined as a distance between mainplanes of the respective parallel plate electrodes when havingirregularities on the surfaces, an average distance between the parallelplate electrode when having concave/convex surfaces, and/or a distancebetween areas of the respective parallel plate electrodes when havingsizes larger than a substrate, which areas are defined by an outerperiphery of the substrate. The distance between the electrodes istypically in a range of 1 to 5 mm, preferably in a range of 1 to 3 mmwhere a thickness of a substrate is typically 0.7 mm.

In some embodiments including the above embodiment, the term “precursor”refers generally to a compound that participates in the chemicalreaction that produces another compound, and particularly to a compoundthat constitutes a film matrix or a main skeleton of a film, whereas theterm “reactant” refers to a compound that is not a precursor andactivates a precursor, modifies a precursor, or catalyzes a reaction ofa precursor, and the term “inert gas” refers to a gas which is not aprecursor nor reactant gas and is inactive or inert when in anon-excited state, but may be active or reactive when in an excitedstate. In some embodiments, the inert gas is not a reactant and includesnoble gases.

In the above, the term “continuously” refers to without interruption inspace (e.g., uninterrupted supply over the substrate), withoutinterruption in flow (e.g., uninterrupted inflow), and/or at a constantrate (the term need not satisfy all of the foregoing simultaneously),depending on the embodiment. In some embodiments, “continuous” flow hasa constant flow rate (alternatively, even through the flow is“continuous”, its flow rate may be changed with time). In someembodiments, in a “continuous” sequence, steps are “continuously”conducted in order without an intervening step except an auxiliary stepor other negligible step, e.g., valve operation, in the context.Continuous feeding of a reactant gas and an inert gas is effective inincreasing purge efficiency particularly under a subatmosphericpressure. The continuous flow can be achieved using a flow-pass system(FPS) which is described later. In some embodiments, the pressure of thereaction chamber is constant throughout steps (i) to (v).

In this disclosure, the term “subatmospheric pressure” refers to apressure lower than atmospheric pressure (about 101 kPa), typically in arange of 15 kPa to 80 kPa, preferably in a range of 15 kPa to 30 kPa. Atsubatmospheric pressure, glow discharge, not arc discharge, can berealized under conditions disclosed in this disclosure.

Accordingly, when the substrate has a trench pattern on which the filmis deposited, properties of a film deposited on a sidewall of the trenchcan be as good as those of a film deposited on a flat surface, even whenthe trench has a high aspect ratio (e.g., 2 to 10, 3 to 5) with a widthof 10 nm to 50 nm, for example.

In some embodiments, subatmospheric PEALD is conducted using aconventional or any suitable PEALD apparatus, i.e., a process oflow-pressure PEALD or other treatment and a process of subatmosphericPEALD or other treatment can be conducted in combination in the samereactor while continuously operating an exhaust system using a vacuumpump. In some embodiments where a low-pressure PEALD apparatus which isoperable under a process pressure of 1 to 10 mTorr, a pressure of thereaction chamber is continuously controlled in a range of 15 kPa to 80kPa by conducting at least one (preferably at least two) of thefollowing operations while running a vacuum pump which exhausts gasesfrom the reaction chamber: (a) passing the exhausting gases through athrottle valve provided downstream of the reaction chamber and upstreamof the vacuum pump, (b) reducing flow of the exhausting gases whilepassing said gases through at least one auto pressure controller (APC)provided downstream of the reaction chamber and upstream of the vacuumpump, (c) supplying ballast gas to a flow of the exhausting gasesdownstream of the reaction chamber and upstream of the vacuum pump, and(d) reducing rotational speed of a motor of the vacuum pump.

In some embodiments, operation (a) is conducted wherein the throttlevalve is an orifice gasket. Alternatively, the throttle valve can be aneedle valve. In some embodiments, operation (b) is conducted whereintwo APCs are provided in series. In some embodiments, operation (c) isfurther conducted wherein the ballast gas is nitrogen gas which issupplied between the two APCs. In some embodiments, operation (d) isconducted wherein the rotational speed of the motor is reduced by aninverter device connected to the motor.

In some embodiments, the RF power is in a range of 0.707 W/cm² to 7.07W/cm² (wattage per area of a substrate), preferably in a range of 1.0W/cm² to 3.0 W/cm². In some embodiments, the RF power has a frequency of1 kHz to 100 MHz, preferably 1 MHz to 50 MHz.

In some embodiments, the film is constituted by silicon or metal oxide,silicon or metal nitride, silicon or metal carbide, silicon or metaloxynitride, or silicon or metal carbonitride.

In some embodiments, the precursor is selected from the group consistingof H_(a)Si_(b)R_(c), R¹ _(a)Si_(b)R² _(c), H_(a)Me_(b), and R¹_(a)Me_(b)R² _(c), wherein R, R¹, and R² are (N(C_(x)H_(y))H)_(z),(N(C_(x)H_(y))₂)_(z), (OC_(x)H_(y))_(z), halogen, OH, or non-cyclic orcyclic C_(x)H_(y) having double or triple bonds, R¹ and R² aredifferent, and a, b, c, x, y, and z are integers. In some embodiments,the precursors include, aminosilane such as bisdimethylaminosilane andbisdiethylaminosilane, silicon halide such asdichlorotetramethyldisilane and dimethyldichlorosilane, and siliconhydrocarbon such as divinyldimethylsilane and phenylsilane, any one ofwhich can be used singly or any two or more of which can be used in anycombination. In some embodiments, in place of silicon, a metal-basedprecursor can be used. As for a metal, Ti, Zr, and/or Al can be used. Insome embodiments, the precursor is constituted by a first precursor anda second precursor which is different from the first precursor, and thefirst precursor and the second precursor are alternately used whenrepeating the cycle of PEALD. In some embodiments, the precursor isconstituted by a first precursor and a second precursor which isdifferent from the first precursor, and step (i) comprises (ia)supplying the first precursor in a pulse to the reaction chamber, andthen (ib) supplying the second precursor in a pulse to the reactionchamber. In some embodiments, three different precursors can be used.

In some embodiments, the reactant is one or more gases selected from thegroup consisting of oxidizing gases (such as oxygen, ozone, carbondioxide, and/or ethanol), nitriding gases (such as ammonia, nitrogen,and/or hydrazine), and hydrogen gas.

In some embodiments, the inert gas is nitrogen gas and/or noble gas, andin some embodiments, the inert gas is solely He, Ar, or a mixture of Heand Ar.

In some embodiments, the method further comprises, after one or morecycles of PEALD, conducting surface treatment comprising: (I)continuously supplying the inert gas to the reaction chamber; (II)continuously controlling the pressure of the reaction chamber in therange of 15 kPa to 80 kPa; and (III) applying RF power for glowdischarge in a pulse to the one of the parallel plate electrodes,wherein no precursor is supplied during the surface treatment. In someembodiments, the surface treatment further comprises continuouslysupplying a reactant to the reaction chamber. For example, the surfacetreatment may be conducted using a gas consisting of an inert gas(excluding a reactant gas and precursor), or a combination of an inertgas and one of the reactant gas: oxygen, nitrogen, a combination ofnitrogen and hydrogen (excluding a precursor). The surface treatment canfurther improve properties such as wet etch rate of a film which isdeposited not only on a flat surface but also on a sidewall of a trench.Since the surface treatment is conducted under a subatmospheric pressurewhich is approximately 100 times, for example, higher than processpressure of conventional surface treatment, plasma density and radicaldensity can be increased by approximately 100 times, thereby improvingfilm properties in a significantly short period of time. The abovesubatmospheric surface treatment can be conducted not only after filmformation by subatmospheric PEALD, but also after film formation bylow-pressure PEALD.

In some embodiments, a method for treating a surface of a film on asubstrate by plasma-enhanced subatmospheric-pressure treatment,comprises: (1) depositing the film on the substrate placed betweencapacitively coupled parallel plate electrodes in an evacuatablereaction chamber by plasma-enhanced atomic layer deposition (PEALD)under a pressure of less than 5 kPa, wherein a distance between theparallel plate electrodes is in a range of 1 mm to 5 mm; and (2) afterone or more cycles of PEALD, continuously conducting a cycle of surfacetreatment comprising: (i) continuously supplying an inert gas to thereaction chamber; (ii) continuously controlling a pressure of thereaction chamber in a range of 15 kPa to 80 kPa; and (iii) applying RFpower for glow discharge in a pulse to one of the parallel plateelectrodes, wherein no precursor is supplied during the surfacetreatment.

In some embodiments, the cycle of the surface treatment furthercomprises continuously supplying a reactant to the reaction chamber. Insome embodiments, step (ii) comprises conducting at least one of thefollowing operations while running a vacuum pump which exhausts gasesfrom the reaction chamber: (a) passing the exhausting gases through athrottle valve provided downstream of the reaction chamber and upstreamof the vacuum pump, (b) reducing flow of the exhausting gases whilepassing said gases through at least one auto pressure controller (APC)provided downstream of the reaction chamber and upstream of the vacuumpump, (c) supplying ballast gas to a flow of the exhausting gasesdownstream of the reaction chamber and upstream of the vacuum pump, and(d) reducing rotational speed of a motor of the vacuum pump.

The embodiments will be explained with respect to the drawings. However,the present invention is not limited to the drawings.

FIG. 2 shows a schematic continuous process sequence of subatmosphericPEALD in one cycle according to an embodiment of the present inventionusing one precursor wherein a cell in gray represents an ON statewhereas a cell in white represents an OFF state, and the width of eachcell does not represent duration of each process. In the sequenceillustrated in FIG. 2, the precursor is supplied in a pulse (“Feed”)using a carrier gas and a dilution gas (collectively referred to as“Inert gas”) which are continuously supplied. This can be accomplishedusing a flow-pass system (FPS) wherein a carrier gas line is providedwith a detour line having a precursor reservoir (bottle), and the mainline and the detour line are switched, wherein when only a carrier gasis intended to be fed to a reaction chamber, the detour line is closed,whereas when both the carrier gas and a precursor gas are intended to befed to the reaction chamber, the main line is closed and the carrier gasflows through the detour line and flows out from the bottle togetherwith the precursor gas. In this way, the carrier gas can continuouslyflow into the reaction chamber, and can carry the precursor gas inpulses by switching the main line and the detour line. FIG. 1Billustrates a precursor supply system using a flow-pass system (FPS)according to an embodiment of the present invention (black valvesindicate that the valves are closed). As shown in (a) in FIG. 1B, whenfeeding a precursor to a reaction chamber (not shown), first, a carriergas such as Ar (or He) flows through a gas line with valves b and c, andthen enters a bottle (reservoir) 20. The carrier gas flows out from thebottle 20 while carrying a precursor gas in an amount corresponding to avapor pressure inside the bottle 20, and flows through a gas line withvalves f and e, and is then fed to the reaction chamber together withthe precursor. In the above, valves a and d are closed. When feedingonly the carrier gas (noble gas) to the reaction chamber, as shown in(b) in FIG. 1B, the carrier gas flows through the gas line with thevalve a while bypassing the bottle 20. In the above, valves b, c, d, e,and f are closed.

Under subatmospheric pressure, efficiency of purging is significantlylow. However, the FPS can compensate for the insufficient purging undersubatmospheric pressure. Further, extremely high flow rate of a dilutiongas such as 10 slm to 60 slm (typically 20 slm to 50 slm) improvesefficiency of purging.

In FIG. 2, the precursor is provided with the aid of a carrier gas(“Inert gas”). Since ALD is a self-limiting adsorption reaction process,the number of deposited precursor molecules is determined by the numberof reactive surface sites and is independent of the precursor exposureafter saturation, and a supply of the precursor is such that thereactive surface sites are saturated thereby per cycle. A plasma fordeposition is generated by applying RF power (“RF”) in a pulse (“RF”) insitu in a reactant gas (“Reactant”) (e.g., an ammonia gas) that flowscontinuously throughout the deposition cycle, while the inert gas isalso continuously fed to the reaction space, without feeding theprecursor, thereby forming a monolayer.

As mentioned above, each pulse or phase of each deposition cycle ispreferably self-limiting. An excess of reactants is supplied in eachphase to saturate the susceptible structure surfaces. Surface saturationensures reactant occupation of all available reactive sites (subject,for example, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage. In some embodiments the pulse time ofone or more of the reactants can be reduced such that completesaturation is not achieved and less than a monolayer is adsorbed on thesubstrate surface. After “Feed”, the reaction space is purged (“Purge1”) where no precursor is fed to the reaction space, while the inert gasand reactant gas are continuously fed to the reaction space, withoutapplying RF power, thereby removing non-chemisorbed precursor and excessgas from the surface of the substrate. After “RF”, the reaction space ispurged (“Purge 2”) where the inert gas and reactant gas are continuouslyfed to the reaction space, without feeding the precursor and withoutapplying RF power to the reaction space, thereby removing by-productsand excess gas from the surface of the substrate. Due to the continuousflow of the reactant gas, and also due to the continuous flow of theinert gas entering into the reaction space as a constant stream intowhich the precursor is injected intermittently or in pulses, purging canbe conducted efficiently to remove excess gas and by-products quicklyfrom the surface of the layer, thereby efficiently continuing multiplePEALD cycles.

Throughout each cycle, the reaction space is controlled atsubatmospheric pressure (“Pressure”). The pressure control can beconducted as follows, for example, so that subatmospheric PEALD can beperformed using a low-pressure PEALD apparatus while continuouslyrunning a vacuum pump or an exhaust system.

FIG. 7 is a schematic representation of a subatmospheric PEALD apparatusfor depositing a dielectric film usable in an embodiment of the presentinvention. Subatmospheric PEALD is conducted in a reactor 31. Thepressure in a reaction chamber 31 is detected and monitored continuouslyor intermittently, and a controller 40 controls the process pressureaccording to a flowchart or algorithm illustrated in FIG. 8, for example(which is explained below). The process pressure can be controlled byany one or more of the following operations: Operation (a) is passingexhausting gases through a throttle valve 34 provided downstream of thereaction chamber 31 and upstream of a vacuum pump 32. When passing theexhausting gases through the throttle valve 34 provided in a pipe c, avalve 35 (e.g., a gate valve, rather than an on-off valve, since pipes band c have an inner diameter of 1.375″ and an outer diameter of 2.16″,for example) is closed. The throttle valve may be an orifice gasket. Thepipe a which bypasses the pipe b is, for example, a ¼″ pipe which issmaller than the pipe b so as to create more pressure loss to reducevacuum force (the degree of vacuum) by the vacuum pump 32. The orificegasket 34 has, for example, an opening having a diameter of about 0.5mm. The throttle valve can be a needle valve which is anopening-adjustable valve.

Operation (b) is reducing flow of the exhausting gases while passingsaid gases through at least one auto pressure controller (APC) 37, 38provided in the pipe c downstream of the reaction chamber 31 andupstream of the vacuum pump 32. By using the APC 37, 38, the vacuumforce (the degree of vacuum) by the vacuum pump 32 can effectively bereduced.

Operation (c) is supplying ballast gas through a pipe d from a ballastgas source 33 to a flow of the exhausting gases downstream of thereaction chamber 31 and upstream of the vacuum pump 32. A valve 36provided in the pipe d is, for example, an air-operated valve whichcontrols a ballast gas flow. In this configuration, the pipe d isconnected to the pipe c between the APC 37 and the APC 38, so that theAPC 37 functions as a check valve which prevents a backflow of theballast gas. The ballast gas is, for example, nitrogen gas, and a flowrate is about 10 L/min to about 100 L/min, typically about 10 L/min toabout 30 L/min. By using the ballast gas, the vacuum force (the degreeof vacuum) by the vacuum pump 32 can effectively be reduced.

Operation (d) is reducing rotational speed of a motor of the vacuum pump32. Operation (d) is conducted wherein the rotational speed of the motoris reduced by an inverter device 39 connected to the motor. By using theinverter device 39 which changes a frequency of current to adjust therotation speed of the motor, the vacuum pump having an exhaust capacityof, for example, about 6,000 L/min can be reduced to about 2,000 L/min.

FIG. 8 is a flowchart illustrating a process sequence of subatmosphericPEALD according to an embodiment of the present invention. Thecontroller 40 stores a program to execute the algorithm. In step 1, thepressure of the reaction chamber 31 is detected and monitored. In step2, the measured pressure is compared with a preset target pressure, andit is determined if the measured pressure is lower than the set value ofthe target pressure. If the measured pressure is lower than the setvalue, in step 3, one or more of operations (a) to (d) which have beenselected are conducted while running the vacuum pump 32. In step 4 whenthis step (operation (a)) is preselected, the controller 40 controls theexhausting gases to pass through the orifice gasket 34 while closing thevalve 35. In step 5 when this step (operation (b)) is preselected, thecontroller 40 controls the APCs 37 and 38 to reduce flow of theexhausting gases. In step 6 when this step (operation (c)) ispreselected, the controller 40 opens the valve 36 to supply the ballastin the pipe c between the APCs 37 and 38. In step 7 when this step(operation (d)) is preselected, the controller 40 reduces the rotationspeed of the motor of the vacuum pump 32.

In some embodiments, the pressure in the reaction chamber is controlledcontinuously at a substantially constant value using the flow-passsystem (FPS) illustrated in FIG. 1B, for example, so that plasmastability can be improved, and also throughput can be improved byeliminating a time period for stabilizing gas flows. The term“substantially” constant or the like may refer to an immaterialfluctuation, a fluctuation that does not materially affect the target orintended properties, or a fluctuation recognized by a skilled artisan asnearly zero, such as less than 10%, less than 5%, or any ranges thereofrelative to the total or the referenced value in some embodiments.

A skilled artisan will appreciate that the apparatus includes one ormore controller(s) (not shown) programmed or otherwise configured tocause the deposition and reactor cleaning processes described elsewhereherein to be conducted. The controller(s) are communicated with thevarious power sources, heating systems, pumps, robotics, and gas flowcontrollers or valves of the reactor, as will be appreciated by theskilled artisan.

The process cycle can be performed using any suitable apparatusincluding an apparatus illustrated in FIG. 1A, for example. FIG. 1A is aschematic view of a PEALD apparatus, desirably in conjunction withcontrols programmed to conduct the sequences described below, usable insome embodiments of the present invention. In this figure, by providinga pair of electrically conductive flat-plate electrodes 4, 2 in paralleland facing each other in the interior 11 (reaction zone) of a reactionchamber 3, applying HRF power (13.56 MHz or 27 MHz) 25 to one side, andelectrically grounding the other side 12, a plasma is excited betweenthe electrodes. A temperature regulator is provided in a lower stage 2(the lower electrode), and a temperature of a substrate 1 placed thereonis kept constant at a given temperature. The upper electrode 4 serves asa shower plate as well, and reactant gas (and noble gas) and precursorgas are introduced into the reaction chamber 3 through a gas line 21 anda gas line 22, respectively, and through the shower plate 4.Additionally, in the reaction chamber 3, a circular duct 13 with anexhaust line 7 is provided, through which gas in the interior 11 of thereaction chamber 3 is exhausted. Additionally, a transfer chamber 5disposed below the reaction chamber 3 is provided with a seal gas line24 to introduce seal gas into the interior 11 of the reaction chamber 3via the interior 16 (transfer zone) of the transfer chamber 5 wherein aseparation plate 14 for separating the reaction zone and the transferzone is provided (a gate valve through which a wafer is transferred intoor from the transfer chamber 5 is omitted from this figure). Thetransfer chamber is also provided with an exhaust line 6. In someembodiments, the deposition of multi-element film and surface treatmentare performed in the same reaction space, so that all the steps cancontinuously be conducted without exposing the substrate to air or otheroxygen-containing atmosphere. In some embodiments, a remote plasma unitcan be used for exciting a gas.

In the apparatus illustrated in FIG. 1A, in order to increase an inertgas flow flowing into the reaction chamber, an inert gas may also beintroduced into the reaction chamber through a side flow line 17, inaddition to the gas flow from the showerhead 4. Alternatively, in placeof the showerhead, only the side flow line is used to introduce theprocess gases, wherein an upper electrode without a shower plate canreplace the showerhead.

In some embodiments, in the apparatus depicted in FIG. 1A, the system ofswitching flow of an inactive gas and flow of a precursor gasillustrated in FIG. 1B (described earlier) can be used to introduce theprecursor gas in pulses without substantially fluctuating pressure ofthe reaction chamber.

In some embodiments, a dual chamber reactor (two sections orcompartments for processing wafers disposed closely to each other) canbe used, wherein a reactant gas and a noble gas can be supplied througha shared line whereas a precursor gas is supplied through unsharedlines.

In some embodiments, the subatmospheric PEALD cycles may be conductedunder the conditions shown in Table 1 below.

TABLE 1 (numbers are approximate) Conditions for subatmospheric PEALDSubstrate temperature 50 to 550° C. (preferably 100 to 400° C.)Electrode gap (a thickness of a 1.0 to 5.0 mm (preferably 1.0 to 3.0 mm)substrate is about 0.7 mm) Pressure 15 to 80 kPa (preferably 15 to 50kPa) Flow rate of reactant gas (continuous) 100 to 3000 sccm (preferably200 to 2000 sccm) Flow rate of carrier gas (continuous) 500 to 5000 sccm(preferably 1000 to 2000 sccm) Flow rate of dilution gas (continuous)0.1 to 3 slm (preferably 0.2 to 2 slm) Flow rate of precursorCorresponding to the flow rate of carrier gas RF power (13.56 MHz) for a300-mm 500 to 5000 W (preferably 1000 to 2000 W) wafer Duration of“Feed” 0.1 to 5 sec. (preferably 0.1 to 1 sec.) Duration of “Purge 1”0.1 to 5 sec. (preferably 0.3 to 1 sec.) Duration of “RF” 0.1 to 10 sec.(preferably 0.5 to 5 sec.) Duration of “Purge 2” 0.1 to 1 sec.(preferably 0.1 to 0.5 sec.) Duration of one cycle 0.4 to 22 sec.(preferably 1 to 12 sec.) Glow rate per cycle (nm/min) 0.1 to 2(preferably 0.3 to 1) on top surface

The above indicated RF power for a 300-mm wafer can be converted toW/cm² (wattage per unit area of a wafer) which can apply to a waferhaving a different diameter such as 200 mm or 450 mm.

Typically, the thickness of the dielectric film to be etched is in arange of about 50 nm to about 500 nm (a desired film thickness can beselected as deemed appropriate according to the application and purposeof film, etc.). The dielectric film may be used for double-patterning.

In some embodiments, the process sequence may be set as illustrated inFIG. 3. FIG. 3 shows a schematic continuous process sequence ofsubatmospheric PEALD in one cycle according to an embodiment of thepresent invention using two precursors wherein a cell in gray representsan ON state whereas a cell in white represents an OFF state, and thewidth of each cell does not represent duration of each process.

In this embodiment, one cycle of subatmospheric PEALD comprises “Feed 1”where a 1^(st) precursor gas (“1^(st) Precursor”) is fed to a reactionspace via a carrier gas (“Inert gas”) which carries the precursorwithout applying RF power to the reaction space, and also, a dilutiongas (together with the carrier gas collectively referred to as “Inertgas”) and a reactant gas (“Reactant”) are fed to the reaction space,thereby chemisorbing the precursor gas onto a surface of a substrate viaself-limiting adsorption, while continuously controlling the processpressure at a subatmospheric pressure; “Purge 1” where no precursor isfed to the reaction space, while the carrier gas, dilution gas, andreactant gas are continuously fed to the reaction space, withoutapplying RF power, thereby removing non-chemisorbed precursor gas andexcess gas from the surface of the substrate while continuouslycontrolling the process pressure; “RF 1” where RF power is applied tothe reaction space while the carrier gas, dilution gas, and reactant gasare continuously fed to the reaction space, without feeding theprecursor, thereby depositing a dielectric layer through plasma surfacereaction with the reactant gas in an excited state while continuouslycontrolling the process pressure; and “Purge 2” where the carrier gas,dilution gas, and reactant gas are continuously fed to the reactionspace, without feeding the precursor and without applying RF power tothe reaction space, thereby removing by-products and excess gas from thesurface of the substrate while continuously controlling the processpressure. In the above, “Feed 1”, “Purge 1”, “RF 1”, and “Purge 2”substantially correspond to “Feed”, “Purge 1”, “RF”, and “Purge 2”illustrated in FIG. 2, respectively. The one cycle of subatmosphericPEALD further comprises similar processes for a 2^(nd) precursor(“2^(nd) Precursor”), which comprises “Feed 2”, “Purge 3”, “RF 2”, and“Purge 4”, which substantially correspond to “Feed 1”, “Purge 1”, “RF1”, and “Purge 2”, respectively. Due to the continuous flow of thecarrier gas entering into the reaction space as a constant stream intowhich the precursor is injected intermittently or in pulses, and due tocontinuous flow of the dilution gas and reactant gas entering into thereaction space as a constant stream, the purging can be conductedefficiently to remove excess gas and by-products quickly from thesurface of the layer, thereby efficiently continuing multiple ALD cycleseven under subatmospheric pressure.

FIG. 4 shows a schematic continuous process sequence of subatmosphericPEALD in one cycle according to another embodiment of the presentinvention using two precursors wherein a cell in gray represents an ONstate whereas a cell in white represents an OFF state, and the width ofeach cell does not represent duration of each process. In this sequence,“Feed 1”, “Purge 1”, “RF”, and “Purge 3” substantially correspond to“Feed”, “Purge 1”, “RF”, and “Purge 2” illustrated in FIG. 2,respectively. In addition, the sequence further comprises “Feed 2” and“Purge 2” for a 2^(nd) precursor (“2^(nd) Precursor”) which are insertedbetween “Purge 1” and “RF”.

FIG. 6 shows a schematic continuous process sequence of subatmosphericsurface treatment in one cycle according to an embodiment of the presentinvention wherein a cell in gray represents an ON state whereas a cellin white represents an OFF state, and the width of each cell does notrepresent duration of each process. The subatmospheric surface treatmentcan be conducted after deposition of a film by the subatmospheric PEALDor low-pressure PEALD. The subatmospheric surface treatment can furtherimprove properties of a film not only deposited on a flat surface butalso deposited at a sidewall of a trench due to high plasma densityunder subatmospheric pressure. In FIG. 6, the sequence comprises: “Gascharge” where an inert gas (“Inert gas”) is continuously fed to thereaction space while continuously controlling the pressure (“Pressure”)at a subatmospheric pressure as discussed in this disclosure, withoutapplying RF power to the reaction chamber and without feeding aprecursor or a reactant gas (alternatively, in another embodiment, areactant gas may be fed); “Stabilize” where process conditions aremaintained until gas flow is stabilized; “RF” where RF power is appliedto the reaction space; and “Purge” where the reaction space is purged.

In some embodiments, subatmospheric surface treatment may be conductedunder conditions shown in Table 2 below.

TABLE 2 (numbers are approximate) Conditions for subatmospheric surfacetreatment Substrate temperature Same as in 1 to 5 subatmospheric PEALDPressure Same as in subatmospheric PEALD Inert gas Same as insubatmospheric PEALD Flow rate of inert gas Same as in subatmosphericPEALD (continuous) RF power (13.56 MHz) for 100 to 5000 W (preferably300 to 3000 W) a 300-mm wafer Duration of “Gas change” 1 to 15 sec.(preferably sec.) Duration of “Stabilize” 2 to 15 sec. (preferably 2 to10 sec.) Duration of “RF” 0.1 to 10 sec. (preferably 0.3 to 5 sec.)Duration of “Purge” 0.1 to 2 sec. (preferably 0.1 to 1 sec.)

The above indicated RF power for a 300-mm wafer can be converted toW/cm² (wattage per unit area of a wafer) which can apply to a waferhaving a different diameter such as 200 mm or 450 mm.

FIG. 5 shows a schematic continuous process sequence of subatmosphericPEALD in one cycle and a schematic process sequence of subsequentsubatmospheric treatment in one cycle according to an embodiment of thepresent invention wherein a cell in gray represents an ON state whereasa cell in white represents an OFF state, and the width of each cell doesnot represent duration of each process. In this sequence, thesubatmospheric PEALD comprises “Feed”, “Purge 1”, “RF”, and “Purge 2”which substantially correspond to those illustrated in FIG. 2,respectively. After repeating the above cycle m times (m is an integerof 1 to 1000, preferably 50 to 200), the subatmospheric surfacetreatment is initiated, which comprises “Gas charge”, “Stabilize”, “RF”,and “Purge 3” which substantially correspond to “Gas charge”,“Stabilize”, “RF”, and “Purge” illustrated in FIG. 6, respectively. Theabove cycle can be repeated n times (n is an integer of 1 to 1000,preferably 1 to 50). A ratio of n/m may be in a range of 1/1000 to 1/1,preferably 1/500 to 1/2.

The present invention is further explained with reference to workingexamples below. However, the examples are not intended to limit thepresent invention. In the examples where conditions and/or structuresare not specified, the skilled artisan in the art can readily providesuch conditions and/or structures, in view of the present disclosure, asa matter of routine experimentation. Also, the numbers applied in thespecific examples can be modified by a range of at least ±50% in someembodiments, and the numbers are approximate.

EXAMPLES Examples 1 to 7

A film was formed on a Si substrate (having a diameter of 300 mm and athickness of 0.7 mm) having trenches with an aspect ratio of 4 (a widthof 25 nm, and a depth of 100 nm) by subatmospheric PEALD using asequence illustrated in FIG. 2, one cycle of which was conducted underthe common conditions shown in Table 3 (process cycle) below using thePEALD apparatus illustrated in FIG. 1A and a gas supply system (FPS)illustrated in FIG. 1B with the specific conditions and sequenceindicated in Table 4.

TABLE 3 (numbers are approximate) Common Conditions for Process CycleCarrier gas and dilution gas Ar Flow rate of carrier gas (continuous) 2slm Precursor pulse 1 sec Purge after precursor feed pulse 2 sec RFpower pulse 1 sec Purge after RF power pulse 1 sec

TABLE 4 (numbers are approximate) Dilu- Temp. Pressure RF Gap Reactant/tion Precursor (° C.) (kPa) (W) (mm) slm (slm) *1 Bisdimethyl- 300 0.4100 12 O₂/0.1 1 aminosilane *2 Dichlorotetra- 400 0.4 200 12 NH₃/2 1mehyldisilane *3 Divinyldimethyl- 300 0.4 100 12 CO₂/0.1 1 silane  4Bisdimethyl- 300 50 1,000 5 O₂/0.1 30 aminosilane  5 Bisdimethyl- 300 501,000 2 O₂/0.1 30 aminosilane  6 Dichlorotetra- 400 30 2,000 2 NH₃/2 50mehyldisilane  7 Divinyldimethyl- 300 50 1,000 2 CO₂/0.1 30 silane

In Table 4, the Example numbers with “*” indicate comparative examples.Each obtained film was evaluated. Table 5 shows the results ofevaluation.

TABLE 5 (numbers are approximate) Sidewall 100:1 DHF Coverage @ 100:1DHF GPC Top WER AR4 Side WER Side/Top (nm/cycle) RI (nm/min) (%)(nm/min) WER Film *1 0.1 1.47 3.8 95 4.8 1.3 SiO *2 0.05 1.88 1.2 95 4.84 SiN *3 0.03 1.71 0.1 60 0.5 5 SiCO  4 0.11 1.45 3.2 95 3.8 1.2 SiO  50.11 1.46 2.9 105 3.0 1.0 SiO  6 0.05 1.96 0.8 97 0.9 1.1 SiN  7 0.041.78 0.1 89 0.1 1.0 SiCO

In Table 4, “GPC” represents growth rate per cycle, “SidewallCoverage@AR4” represents a percentage of thickness of film deposited ona sidewall relative to thickness of film deposited on a blanket surfaceat a trench having an aspect ratio of 3, “RI” represents refractiveindex, and “100:1 DHF Top/Side WER” represents wet etch rate of a topfilm/side film using a solution of 100:1 DHF (diluted hydrogenfluoride).

As shown in Table 5, according to the subatmospheric PEALD disclosedherein, the target films could be deposited as if the films weredeposited by low-pressure PEALD. Further, the films deposited by thesubatmospheric PEALD had excellent conformality (typically about 90% orhigher) and excellent uniformity of film properties (typically a ratioof side/top WER of 1.2 or less) in the trench, regardless of the type offilm (Examples 4 to 7). Particularly when depositing the filmsconstituted by SiN or SiCO where low plasma density at the sidewall wasa problem in the low-pressure PEALD, resulting in uneven properties ofthe films deposited at the sidewall and the top surface (Examples 2 and3), by the subatmospheric PEALD, films with excellent uniformity weredeposited (Examples 6 and 7). Further, in the subatmospheric PEALD, whenthe gap between the electrodes was as small as about 2 mm (Example 5),even higher uniformity of film properties was achieved as compared withwhen the gap was about 5 mm (Example 4).

Reference Examples

In reference examples, ignition of a plasma under subatmosphericpressure was investigated under the conditions used in Example 5 aboveexcept for the inert gas (dilution gas), the inert gas flow rate, theoxygen flow rate, and the process pressure. The results are shown inFIG. 9. FIG. 9 shows minimum RF power required for ignition of a plasmaat pressures of 0.5 kPa and 30 kPa when varying concentration of oxygenin a reactant gas, wherein (a) shows when the reactant gas contains He,and (b) shows when the reactant gas contains Ar. As shown in FIG. 9,when He was used as the inert gas as compared with Ar, a plasma wasignited more stably at a lower RF power wherein when the oxygenconcentration was 4% and 7% (typically 1% or more but less than 10%), aplasma was stably ignited by an RF power of 500 W even undersubatmospheric pressure, and when the oxygen concentration was 10%, aplasma was stably ignited by an RF power of 1,000 W. However, when theoxygen concentration was 0% (typically 1% or less), both He and Ar couldignite a plasma at an RF power of 500 W. Thus, when a high oxygenconcentration (typically 1% or higher) is required in subatmosphericPEALD, by using He as the inert gas, a plasma can be stably ignited.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

We/I claim:
 1. A method for depositing a film by plasma-enhancedsubatmospheric-pressure atomic layer deposition, comprising: placing asubstrate between capacitively coupled parallel plate electrodes in anevacuatable reaction chamber, wherein a distance between the parallelplate electrodes is in a range of 1 mm to 5 mm; and depositing a filmhaving a desired thickness on the substrate by plasma-enhanced atomiclayer deposition (PEALD), each cycle of which comprises: (i) supplying aprecursor in a pulse to the reaction chamber; (ii) continuouslysupplying a reactant to the reaction chamber; (iii) continuouslysupplying an inert gas to the reaction chamber; (iv) continuouslycontrolling a pressure of the reaction chamber in a range of 15 kPa to80 kPa; and (v) applying RF power for glow discharge in a pulse to oneof the parallel plate electrodes, wherein the pulse of supplying theprecursor and the pulse of applying RF power do not overlap.
 2. Themethod according to claim 1, wherein step (iv) comprises conducting atleast one of the following operations while running a vacuum pump whichexhausts gases from the reaction chamber: (a) passing the exhaustinggases through a throttle valve provided downstream of the reactionchamber and upstream of the vacuum pump, (b) reducing flow of theexhausting gases while passing said gases through at least one autopressure controller (APC) provided downstream of the reaction chamberand upstream of the vacuum pump, (c) supplying ballast gas to a flow ofthe exhausting gases downstream of the reaction chamber and upstream ofthe vacuum pump, and (d) reducing rotational speed of a motor of thevacuum pump.
 3. The method according to claim 2, wherein operation (a)is conducted wherein the throttle valve is an orifice gasket.
 4. Themethod according to claim 2, wherein operation (b) is conducted whereintwo APCs are provided in series.
 5. The method according to claim 4,wherein operation (c) is further conducted wherein the ballast gas isnitrogen gas which is supplied between the two APCs.
 6. The methodaccording to claim 2, wherein operation (d) is conducted wherein therotational speed of the motor is reduced by an inverter device connectedto the motor.
 7. The method according to claim 1, wherein the RF poweris in a range of 0.707 W/cm² to 7.07 W/cm².
 8. The method according toclaim 1, wherein the pressure of the reaction chamber is constantthroughout steps (i) to (v).
 9. The method according to claim 1, whereinthe substrate has a trench pattern on which the film is deposited. 10.The method according to claim 1, wherein the film is constituted bysilicon or metal oxide, silicon or metal nitride, silicon or metalcarbide, silicon or metal oxynitride, or silicon or metal carbonitride.11. The method according to claim 1, wherein the precursor is selectedfrom the group consisting of H_(a)Si_(b)R_(c), R^(l) _(a)Si_(b)R² _(c),H_(a)Me_(b), and R^(l) _(a)Me_(b)R² _(c), wherein R, R¹, and R² are(N(C_(x)H_(y))H)_(z), (N(C_(x)H_(y))₂)_(z), (OC_(x)H)_(z), halogen, OH,or non-cyclic or cyclic C_(x)H_(y) having double or triple bonds, R¹ andR² are different, and a, b, c, x, y, and z are integers.
 12. The methodaccording to claim 1, wherein the precursor is constituted by a firstprecursor and a second precursor which is different from the firstprecursor, and the first precursor and the second precursor arealternately used when repeating the cycle of PEALD.
 13. The methodaccording to claim 1, wherein the precursor is constituted by a firstprecursor and a second precursor which is different from the firstprecursor, and step (i) comprises (ia) supplying the first precursor ina pulse to the reaction chamber, and then (ib) supplying the secondprecursor in a pulse to the reaction chamber.
 14. The method accordingto claim 1, wherein the reactant is one or more gases selected from thegroup consisting of oxidizing gases, nitriding gases, and hydrogen gas.15. The method according to claim 1, wherein the inert gas is solely He,Ar, or a mixture of He and Ar.
 16. The method according to claim 1,further comprising, after one or more cycles of PEALD, conductingsurface treatment comprising: continuously supplying the inert gas tothe reaction chamber; continuously controlling the pressure of thereaction chamber in the range of 15 kPa to 80 kPa; and applying RF powerfor glow discharge in a pulse to the one of the parallel plateelectrodes, wherein no precursor is supplied during the surfacetreatment.
 17. The method according to claim 16, wherein the surfacetreatment further comprises continuously supplying a reactant to thereaction chamber.
 18. A method for treating a surface of a film on asubstrate by plasma-enhanced subatmospheric-pressure treatment,comprising: depositing the film on the substrate placed betweencapacitively coupled parallel plate electrodes in an evacuatablereaction chamber by plasma-enhanced atomic layer deposition (PEALD)under a pressure of less than 5 kPa, wherein a distance between theparallel plate electrodes is in a range of 1 mm to 5 mm; and after oneor more cycles of PEALD, continuously conducting a cycle of surfacetreatment comprising: (i) continuously supplying an inert gas to thereaction chamber; (ii) continuously controlling a pressure of thereaction chamber in a range of 15 kPa to 80 kPa; and (iii) applying RFpower for glow discharge in a pulse to one of the parallel plateelectrodes, wherein no precursor is supplied during the surfacetreatment.
 19. The method according to claim 18, wherein the cycle ofthe surface treatment further comprises continuously supplying areactant to the reaction chamber.
 20. The method according to claim 18,wherein step (ii) comprises conducting at least one of the followingoperations while running a vacuum pump which exhausts gases from thereaction chamber: (a) passing the exhausting gases through a throttlevalve provided downstream of the reaction chamber and upstream of thevacuum pump, (b) reducing flow of the exhausting gases while passingsaid gases through at least one auto pressure controller (APC) provideddownstream of the reaction chamber and upstream of the vacuum pump, (c)supplying ballast gas to a flow of the exhausting gases downstream ofthe reaction chamber and upstream of the vacuum pump, and (d) reducingrotational speed of a motor of the vacuum pump.